Table 1.2 Frequency Band Designations Label Nominal Frequency Range Itu—region 2 Line-of-sight Propagation and the Radio Horizon

نویسنده

  • John S. Seybold
چکیده

As wireless systems become more ubiquitous, an understanding of radiofrequency (RF) propagation for the purpose of RF planning becomes increasingly important. Most wireless systems must propagate signals through nonideal environments. Thus it is valuable to be able to provide meaningful characterization of the environmental effects on the signal propagation. Since such environments typically include far too many unknown variables for a deterministic analysis, it is often necessary to use statistical methods for modeling the channel. Such models include computation of a mean or median path loss and then a probabilistic model of the additional attenuation that is likely to occur. What is meant by “likely to occur” varies based on application, and in many instances an availability figure is actually specified. While the basics of free-space propagation are consistent for all frequencies, the nuances of real-world channels often show considerable sensitivity to frequency. The concerns and models for propagation will therefore be heavily dependent upon the frequency in question. For the purpose of this text, RF is any electromagnetic wave with a frequency between 1MHz and 300GHz. Common industry definitions have RF ranging from 1MHz to about 1GHz, while the range from 1 to about 30GHz is called microwaves and 30– 300GHz is the millimeter-wave (MMW) region. This book covers the HF through EHF bands, so a more appropriate title might have been Introduction to Electromagnetic Wave Propagation, but it was felt that the current title would best convey the content to the majority of potential readers.

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تاریخ انتشار 2005